"PAYING NOT TO GO TO THE GYM"

id – id of a person
time – first date of a month by numbers of days since AD (you can use as.Date(df$variable, origin = '0000-01-01') to transform to date format)
attend – number of monthly attendances
club – id of health club
contract - contract type 
=0 if no contract
=1 if monthly
=2 if annual
=7 if contract frozen or cancelled in the middle of month
=20 if at most two months of transition (with no payment) between end of annual contract and subsequent contract
=70 if defaulted (cancelled due to non-payment for the month)
=77 if intervening month between two contracts with no payment (usually only one month)
imprice - imputed price by contract
trprice - price in the billing system
init - initial fee paid
month - month of observation counted since April 1997
begatt - beginning of April 1997 in number of days since AD
endatt - the last month in which attendance is observed
dlocker - rent a locker